OF COURSE and ABSOLUTELY
we would say they are a little "sharp"
of course suggests that only an idiot cannot see this
absolutely is slightly better but it suggests that there is no argument, no possibility of disagreement.
It would be better to say, Yes, I agree, I think so, I agree with you, I believe so. Each of which is agreeing without any "edge" but YES is the easiest and the cleanest.
The other issue is how do you say NO. Again it can be sharp, so you can soften it the same way, "no, I don't think so", "perhaps not", "I'm sorry but I have to disagree with you", "we will have to agree to disagree" even "no, I have to disagree with you" is softer than NO.
avoid, you are correct, as it suggests the person is a teacher of great wisdom